The present invention relates to a data storing system which utilizes a disk unit, and more particularly to the data storing system and the data transfer method which utilize a small-scaled disk unit provided with such a data compressing mechanism as enabling to equivalently increase a storage capacity of a disk.
In a conventional disk subsystem provided with a plurality of small disks and being connected to a host computer, it is known that data compression needs to be carried out for equivalency increasing the capacity of a disk. As a known method for compressing data, a compressing device, provided in a control unit shared by the plurality of disk units, operates to compress data records sent from the host computer and store the compressed data in a predetermined disk unit. This method is described in the publication PCT International No. WO91/20076 (Dec. 26, 1991), for example.
In the aforementioned art, however, the compressing device for compressing data and a cache memory for destaging data to the disk unit or staging data from the disk unit are both provided in the control unit shared by those disk units. Hence, the management of compressed data for those disk units is concentrated on the disk compressing device. This means that breakage of management information for data compression leads to breakage of all the data on the subsystems.